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An Aerospace Solution to Leading Edge Erosion
15th January 2019 Peter Greaves
GLASGOWORE Catapult
Agenda
• Leading Edge Erosion• Introduction to LEFT Project• Methodology
• Modelling• Experimental
• Results• Conclusions
• Leading edge erosion is caused by raindrops impacting the leading edge near to the tip of the blade, where the local velocity can be close to 100m/s (225mph)
• It is a big problem for the industry (their biggest on blades according to a survey carried out among OEMs and owner operators)
• It costs the industry in two ways:• the aerodynamic performance
decreases as erosion gets worse• Repairs need to be carried out
approximately every 5 years• 108 turbines x 6 days at €100k per day for a
jack up rig is €65m in vessel hire, before lost revenue and the cost of repairs has been accounted for!
Leading Edge Erosion
• If the speed limit of leading edge erosion is removed then tip speeds could increase to 120m/s or more
• A 30% increase on current speeds!• A nacelle mass trend derived from a survey of
current nacelles has shown that the estimated nacelle mass for a 20MW turbine would be:
• 1025t at 90 m/s• 815t at 120 m/s• This would lead to a substantial decrease in
tower cost as well as nacelle cost• Jamieson et al [1] demonstrated a turbine CAPEX
reduction of 20% for a 5MW turbine when increasing the tip speed and moving to a downwind rotor
• Dykes et al [2] demonstrated a 5.5% reduction in LCOE by moving from 80 m/s to 100m/s flexible blade
Benefits of Higher Tip Speeds
y = 28,694x + 172442
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100 000
200 000
300 000
400 000
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600 000
700 000
800 000
900 000
- 5 000 10 000 15 000 20 000 25 000
Nac
elle
Mas
s [k
g]
Rated Torque [kNm]
ProductionTurbines
[1] Jamieson P (2009) Light Weight, High Tip Speed Rotors for Offshore. EWEC 2009, Stockholm.[2] Dykes K, Platt A, Guo Y, Ning A, King R, Parsons T, Petch D, Veers P and Resor B (2014) Effect of Tip Speed Constraints on the Optimised Design of a Wind Turbine, NREL TP-50000-61726
• The LEFT project is a collaboration between:• Radius Aerospace UK• Performance Engineered Solutions Ltd• The Offshore Renewable Energy Catapult
• It aims to transfer the use of electroformed Ni-Co leading edge protection from the aerospace industry to wind turbines
• The Ni-Co solution has demonstrated extremely good rain erosion performance:
• It lasts for 85 hours in the ORE Catapult rain erosion rig at 173 m/s
• Typical solutions last for around 15 hours at 120 m/s• However, it will be challenging to integrate with wind turbine
blades:• The alloy has high relative stiffness compared to the
blade • Lightning protection
• The LEFT project aims to address these issues
The LEFT (Leading Edge for Turbines) Project
Adhesive Validation Methodology
DTU 10MW Blade
Extreme Loads
Nodal displacements
Displacements/Moments
Cohesive zone properties
Adhesive stress
Global and Sub-Models
• The test rig was designed and built by PES with rig control using a Raspberry Pi developed by ORE Catapult
• The rig is based on a design by Sorenson et al [3] and applies pure bending moments to the ends of the specimen
• Enables steady crack growth in mode 1 and mode 2
• Calculated values are not dependent on the crack length
• The crack length and angle of the arms were determined using a custom image processing algorithm developed in OpenCV
Fracture Mechanics Rig
𝐽𝐽𝑒𝑒𝑒𝑒𝑒𝑒 = 1 − 𝜐𝜐221 𝑀𝑀1
2 − 𝑀𝑀22 − 6𝑀𝑀1𝑀𝑀2
4𝐵𝐵2𝐻𝐻3𝐸𝐸[3] Sorenson B (2004) A General Mixed Mode Fracture Mechanics Test Specimen, DTU Report
Fracture Mechanics Testing
-100 0 100 200 300 400 500 600
Time (s)
-40
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0
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Mom
ent (
Nm
)
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-10
0
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Cla
mp
angl
e (d
eg)
EpoxyEpoxyEpoxyEpoxyEpoxyEpoxyEpoxyEpoxy
• The experimental tests have been modelled in ANSYS:
• SOLID185 elements for adhesive and substrate
• INTER205 elements with bi-linear cohesive zone model
• BEAM188 Beam elements connect remote point at which beam angular displacements are applied to the substrate nodes
• The STP Adhesive proved very difficult to model in mode 2 because of its very low modulus
Finite Element Modelling Approach
Epoxy Adhesive Results
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Time (s)
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Frac
ture
Res
itanc
e J
R (J
/m2
)
Sample 6 - 3M DP490 - Mode 1 Fracture Toughness
Sample 7 - 3M DP490 - Mode 1 Fracture Toughness
Sample 7 - 3M DP490 - Mode 1 Fracture Toughness (Simulation)
Sample 7 - 3M DP490 - Mode 1 Fracture Toughness (Simulation - Thin Assumption)
0 100 200 300 400 500 600
Time (s)
0
500
1000
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Frac
ture
Res
itanc
e J
R (J
/m2
)
Sample 8 - 3M DP490 - Mode 2 Fracture Toughness
Sample 9 - 3M DP490 - Mode 2 Fracture Toughness
Sample 8 - 3M DP490 - Mode 2 Fracture Toughness (Simulation)
Sample 8 - 3M DP490 - Mode 2 Fracture Toughness (Simulation - Thin Assumption)
EpoxyEpoxyEpoxyEpoxy
EpoxyEpoxyEpoxyEpoxy
Silane Terminated Polymer Adhesive Results
0 50 100 150 200 250 300 350 400
Time (s)
0
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300
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Frac
ture
Res
itanc
e J
R (J
/m2
)
Sample 12 - Sikaflex 953 - Mode 1 Fracture Toughness
Sample 13 - Sikaflex 953 - Mode 1 Fracture Toughness
Sample 12 - Sikaflex 953 - Mode 1 Fracture Toughness (Simulation)
Sample 12 - Sikaflex 953 - Mode 1 Fracture Toughness (Simulation - Thin Assumption)
0 100 200 300 400 500 600 700 800 900
Time (s)
0
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5000
Frac
ture
Res
itanc
e J
R (J
/m2
)
Sample 14 - Sikaflex 953 - Mode 2 Fracture Toughness
Sample 15 - Sikaflex 953 - Mode 2 Fracture Toughness
Sample 15 - Sikaflex 953 - Mode 2 Fracture Toughness (Simulation)
Sample 15 - Sikaflex 953 - Mode 2 Fracture Toughness (Simulation - Thin Assumption)
STP STP STP STP
STP STP STP STP
Critical Load Case/ Position for Sub-Model
66 68 70 72 74 76 78 80 82 84 86
Distance of Submodel from Root (m)
0
2
4
6
8
10
12
14
Max
Von
Mis
es S
tress
in A
dhes
ive
(MPa
)
10 7
Flap Max
Edge Max
Flap Min
Edge Min
Combined
Sub-Model Results: Epoxy Adhesive
Sub-Model Results: STP Adhesive
• A blade meshing tool has been developed which can generate a global solid mesh of the blade and a detailed solid mesh of the tile system
• A model chain has been developed which can accurately predict the adhesive stresses in the Ni-Co tile system
• It can also be used with more detailed models developed from CAD as long as they occupy the same position in space as the global blade mesh
• The next steps are:• Produce a demonstrator of the leading edge system• Investigate how the interface between tiles affects
the stress• Look at certification• Integrate the tile into the blade lightning system
Conclusions
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